1. Field of the Invention
The present invention relates to a method of preparing highly ordered mesoporous silica nanoparticles, which when compared to conventional porous silicas are superior in diffusion rate and reactivity, are capable of being more easily recycled after having been used as the catalysts, solid suppoters and become inactivated more slowly.
2. Description of the Related Art
Porous material mainly is used as a catalyst or solid supporter because of its large surface area. Such a porous material is classified depending on its pore size into the microporous materials having pores less than 2 nm, the mesoporous materials having pores of 2-50 nm, and the macroporous materials having pores exceeding 50 nm. Synthesis of a series of mesoporous materials including MCM-41 and MCM-48 called the M41 family by researchers of Mobile Corporation and in 1992 was published. Also, a mesoporous material known as SBA-15 is being independently synthesized from a layer material similar to MCM-41 by researchers at Santa Barbara. These mesoporous materials have mesopores regularly arranged with a uniform pore diameter of 2-10 nm, have a large surface area (700-1500 m2/g), and have chemical and thermal stability. Because the mesoporous material acting as a porous molecular sieve material has fine pores having a uniform size and which are regularly arranged, it is able to selectively separate and adsorb materials at the molecular level. Moreover, the mesoporous material is very advantageous in terms of enabling the control of a molecule within the pores thereof, and thus it has been widely utilized to function as a catalyst or a catalyst support in chemical reactions. In addition, there are methods of synthesizing other types of mesoporous materials such as MSU, FSM and so on. Most mesoporous materials have a particle size in the micro scale. In recent research related thereto, mesoporous silica nanoparticles which are regularly arranged and in which the shape of the particles may be controlled have been synthesized.
A method of preparing the highly ordered mesoporous silica nanoparticles containing having platinum nanoparticles incorporated therein was published in 2004. This method is carried out in a manner such that platinum nanoparticles are synthesized in the presence of polypyrrolidone (PVP) and dispersed in ethanol, in which a sol-gel reaction of a silica precursor for example tetraethylorthosilicate (TEOS) is then induced in the presence of a surfactant for example cetyltrimethylammonium bromide (CTAB), after which the CTAB is removed, thus synthesizing mesoporous silica nanoparticles having platinum nanoparticles incorporated in the central portions thereof. In addition, a method of preparing mesoporous silica nanoparticles has been devised, which includes forming a mesoporous silica coating layer around hematite having a size of about 150 nm synthesized in an aqueous solution phase, and reducing hematite using hydrogen, thereby synthesizing mesoporous silica nanoparticles in which magnetic particles are incorporated in the silica coating layer thereof. In addition, Victor Lin who is an Iowa State University Professor synthesized mesoporous silica nanoparticles using a synthesis method different from the above and which enables the size of the particles to be more simply controlled.
In accordance with the synthesis method of Professor Victor Lin based on the MCM-41 method, nano-sized mesoporous silica nanoparticles are prepared in such a way that TEOS is added with the use of a surfactant for example CTAB and an ionic functional group for example organotrimethoxysilane in a basic atmosphere so that a sol-gel reaction occurs. The synthesis method for preparing the nanoparticles used in the present research is based on the SBA-15 discovered by researchers at Santa Barbara. Through room-temperature synthesis rather than relatively difficult high-temperature synthesis, nanoparticles which are rapidly and systematically arranged may be obtained. The aforementioned three methods are problematic in that only the part of the nanoparticles prepared in the aqueous solution or ethanol phase may be limitedly used to produce mesoporous silica nanoparticles. Furthermore, in the case where the nanoparticles are prepared in the organic solvent at high temperature, it is difficult to synthesize mesoporous silica nanoparticles having nanoparticles incorporated therein. This is because the sol-gel reaction of the silica precursor should be induced in the aqueous solution phase to form the mesoporous silica coating layer around the nanoparticles synthesized in the organic solvent, but the nanoparticles synthesized in the organic solvent have a hydrophobic surface and are dispersed in the non-polar organic solvent, thus making it difficult to disperse them again in the polar aqueous solution.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.